Known systems for multi-level control, e.g. volume control or screen/light brightness control in consumer electronics products, often use circular touch-pads or capacitive linear sliders (frequently mounted above the keyboard in notebooks), or they are using the touch information from a generic notebook touchpad when the finger is moving in a dedicated slider area on the right border of the touchpad.
These sensors provide absolute position information about the finger tip, and hence the finger tip's angle on the circular touchpad or the position on the slider—information that can be mapped directly or differentially to a control level in a straight forward way.
In particular for the touch wheel it is important that the fingertip and the wheel's geometric center build an angle with a reference point on the wheel, and this angle can be evaluated.
When it comes to the recognition of circle gestures without a fix geometric center position, determining an angle in the circle movement is no longer straight forward. This is the case, for example, for a generic non-circular touchpad, with 2D/3D free-air gestures using near-field capacitive sensor systems, or with mid/far field sensor systems like video or infrared camera systems.
Consider a circle movement which can either be clockwise or counter-clockwise, and we do not limit it to have a fix start or stop position. At each time during the circle movement, for real-time application we can only evaluate data acquired up to the presence, i.e. only partial gesture patterns. Without knowing the drawn circle's center, in the beginning of the movement the detection unit cannot tell the direction of the circle: For example, a left-right movement appears in the top of a clockwise circle but also in the bottom of a counter-clockwise circle.